Former House Speaker Newt Gingrich’s biggest financial backer, billionaire Las Vegas casino tycoon and staunch Israel promoter Sheldon Adelson, is proving a mixed blessing with GOP voters for his favorite candidate, but to date Mr. Gingrich’s presidential rivals have studiously refrained from making the donor a campaign issue.

Mr. Adelson, whose gambling empire extends from Las Vegas to Macau and Singapore, and his wife have pledge a combined $10 million so far to the “super PAC” Winning Our Future in support of Mr. Gingrich’s presidential campaign.

But even as the new super PACs rewrite the rules for campaign financing this election cycle and candidates routinely call one another to task for “independent” attack ads, none of Mr. Gingrich’s rivals has to tried to play up his heavy reliance on a single donor and a donor whose business background and pet cause could cause problems for Mr. Gingrich with some Republican primary voters.

“It’s a dangerous game for any other GOP candidate or super PAC to start attacking the money sources of another [candidate],” said Eric Sapp, American Values Network executive director. “They are all messy and know voters don’t like idea of super PACs. So there is huge risk that if they focus spotlight on other guys’ super PAC, it could reverberate back on them.”

Mr. Sapp said that is why candidates haven’t so raised the issues in the debates and, he adds, “they probably won’t.”

GOP consultant and fundraiser Steve Gordon, an Adelson admirer, thinks former Massachusetts Gov. Romney has plenty of incentive the leave the Adelson connection alone, even as he has launched harshly critical attacks on Mr. Gingrich’s record and temperament in recent debates.

While many social conservatives disapprove of gambling, evangelical voters in general share Mr. Adelson’s strong attachment to Israel and its survival, Mr. Gordon noted.

“I am perfectly willing to predict that Mitt’s campaign will stay away from these issues, as will the super PAC supporting Mitt Romney,” he said.

But some say Democrats may not be so reluctant to raise questions if Mr. Gingrich is the nominee in November.

“If Romney doesn’t use the Adelson issue, Democrats surely will,” said Merrill Matthews, an evangelical who is director of the Council for Affordable Health Insurance. “While a lot of the public is upset with the notion that a handful of wealthy Wall Street types which Romney is being painted as - are profiting at the expense of the middle class, I think even more people would be upset with the notion that a handful of wealthy people can control the direction of an election, or in this case a primary.”

Both favored relocating the U.S. embassy from Tel Aviv to Jerusalem, a move resisted by a long succession of U.S. administrations as too provocative in the Muslim and Arabic-speaking world. Mr. Gingrich now says he would make the move within a week of taking over the Oval Office.

Richard Land, president of the Ethics and Religious Liberty Commission of the Southern Baptist Convention, has said the source of Mr. Adelson’s fortune in legalized gambling was “discomforting.” Born-again Christian evangelicals are divided over support for Mr. Gingrich and former Pennsylvania Sen. Rick Santorum, with Mr. Romney and Ron Paul also picking up some religious right support.

But Mr. Sapp predicted the issue would not prove critical in the race.

“It’s a weakness but one that will be hard for Romney to exploit because he’s not trusted by anti-gambling evangelicals and doesn’t have good validators to go on the offensive,” said Mr. Sapp. “The Religious right doesn’t want him, so they won’t validate those attacks.”

As press attention focused on Mr. Adelson’s hefty financial support in recent weeks, Mr. Gingrich has strongly defended his leading donor, saying that among their common bonds are Mr. Adelson’s concern about Israel and the threat of a nuclear Iran.

Mr. Gingrich said last week Mr. Adelson “very deeply concerned about the survival of Israel.” He said the only promise he had given in return was “that I would seek to defend the United States and United States allies.”